Everyone's point of view has been very helpful. I think on this trip I'll get in Cancun dives including a PADI course (drift, photography, navigation, deep diver - one of those). Manta Divers is just down the street from the hotel and reviews seem good. Your input has inspired me to plan a future trip just to Cozumel to do many dives there. It's semi-inexpensive from Atlanta to get there.
Thanks again!
I'd do the same thing. Getting to spend multiple days diving Cozumel will show you why so many people return to Cozumel over and over again.